The invention relates to a catheter assembly and a method for inserting a cannula useful for the introduction of nutrients or medication, or the extraction of fluids from a living subject. The catheter assembly more particularly comprises a cannula, needle and catheter inserter which allows the selection of the desired length of cannula to be inserted. The method particularly relates to a method of inserting a cannula into a living subject to a desired length.
A number of catheter assemblies are known for introduction of a polymeric cannula into a vein, artery or cavity of a living subject for infusion or extraction of fluids.
In one method, a steel needle is sized to fit within the duct of a cannula and is inserted from the proximal end of the cannula so that the needle exits the distal end. The needle is then inserted into the living subject after which the needle is removed from the cannula, leaving the cannula behind with at least its distal end in the subject. Additional tubing can be attached thereto or medicaments or nutrients can be caused to flow through the cannula into the subject.
In order to prevent the needle from sliding relative to the cannula on insertion, several catheter inserters have been developed which aid the person inserting the cannula to prevent such sliding. This also provides a way to control the cannula without contaminating it. Inserters of a type comprising a device having a pair of winged members which when folded up will pinch the cannula and the needle and prevent motion between them during insertion of the cannula. See, for example, U.S. Pat. No. 3,537,541 to Beck et al and 3,589,361 to Loper et al and East German Pat. No. 67,214 to Wirbatz et al. Generally, a relatively stiff cannula of a material such as Teflon (from DuPont) is fixed to the distal end of the inserter for insertion into the subject while a flexible tubing (e.g. polyvinyl chloride) is attached to the proximal end of the inserter in flow communication with the cannula. See also U.S. Pat. Nos. 4,194,504; 4,198,973; 4,192,304; 4,192,305; 4,300,553; 4,388,074; 4,445,893; 4,353,369; and 4,326,519. The relatively stiff cannula can cause trauma to the body tissues it contacts, especially over extended periods of time.